Printer-processors can be referred to as one of popular image recording apparatuses, which form a latent image on photosensitive recording paper by exposing it to light beams as modulated in intensity based on digital image data. The digital image data are obtained through photo-electrical scanning of an image recorded on photographic film, or by reading them out of a storage medium like a memory card. The printer-processor also processes the recording paper for development, and then dries the paper to produce a photo print. The advantage of such a digital printer-processor is that it can process image data to correct color balance and sharpness, so as to improve the image quality of the photo print.
In the field of the image recording apparatus, many technologies for recording images on opposite sides of recording paper have recently been disclosed, in order to be adaptable to user's needs for diversity and efficient use of recording paper.
Japanese Laid-open Patent Application Hei 5-338274 discloses a both-side printing method which uses a recording device and a turnover device for turning the recording paper in a loop. An image is recorded on one side of the recording paper as it is conveyed in a forward direction. After turning the recording paper over through the turnover device, another image is recorded on the other side as the recording paper is moved in an opposite direction.
Japanese Laid-open Patent Application 2003-266803 discloses a both-side printing method which uses two recording devices and a turnover device placed between these recording devices. An image is recorded on one side of the recording paper by the first recording device. After turning the recording paper over through the turnover device, another image is recorded on the other side by the second recording device.
According to the former prior art, since the recording paper is moved in opposite directions during the printing, it is necessary to convey the recording paper with high accuracy in both directions, in order to record images properly. The demand for high accuracy in paper-transportation will raise the cost. Moreover, because this method does not allow printing on the next sheet of recording paper so long as the foregoing sheet is subjected to the both-side printing, it is hard to improve the processing efficiency.
On the other hand, because the recording device of the digital printer uses a laser exposure unit, and the laser exposure unit is fairly expensive, using two recording devices, like in the latter prior art, is not preferable in terms of cost.
Moreover, in the latter prior art, since the two recording devices are arranged side by side along a paper passageway, the printer for this method must be pretty large in scale.